Dependency injection patterns in Vue - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to provide a value using Vue's provide function.

Vue

<script setup>
import { provide } from 'vue'
const message = 'Hello from provider'
provide([1], message)
</script>

Drag options to blanks, or click blank then click option'

A'messageKey'

Bmessage

Cinject

Dref

Attempts:

3 left

💡 Hint

Common Mistakes

Using the value instead of a key as the first argument.

Using inject instead of provide.

The provide function needs a key as the first argument to identify the value. Here, 'messageKey' is the key used to provide the message.

2fill in blank

medium

Complete the code to inject the provided value using Vue's inject function.

Vue

<script setup>
import { inject } from 'vue'
const receivedMessage = inject([1])
</script>

Drag options to blanks, or click blank then click option'

Aref

Bmessage

Cprovide

D'messageKey'

Attempts:

3 left

💡 Hint

Common Mistakes

Using the value instead of the key.

Using provide instead of inject.

The inject function requires the same key used in provide to receive the value. Here, 'messageKey' is the key.

3fill in blank

hard

Fix the error in the code to correctly inject a default value if the key is not provided.

Vue

<script setup>
import { inject } from 'vue'
const count = inject('countKey', [1])
</script>

Drag options to blanks, or click blank then click option'

Anull

B0

C'0'

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string '0' instead of number 0.

Using undefined which means no default.

The second argument to inject is the default value if the key is not found. Here, 0 is a number default count.

4fill in blank

hard

Fill both blanks to provide and inject a reactive value using Vue's ref.

Vue

<script setup>
import { ref, provide, inject } from 'vue'
const count = ref(0)
provide([1], count)
const injectedCount = inject([2])
</script>

Drag options to blanks, or click blank then click option'

A'countKey'

Bcount

C'countKeyInjected'

Attempts:

3 left

💡 Hint

Common Mistakes

Using different keys for provide and inject.

Using the variable name instead of a string key.

Both provide and inject must use the same key string to share the reactive count value. Here, 'countKey' is used for both.

5fill in blank

hard

Fill all three blanks to create a reactive object, provide it, and inject it in a child component.

Vue

<script setup>
import { reactive, provide, inject } from 'vue'
const state = reactive({ count: 0 })
provide([1], state)
const injectedState = inject([2])
console.log(injectedState[3])
</script>

Drag options to blanks, or click blank then click option'

A'stateKey'

Bstate

C.count

D'stateKeyInjected'

Attempts:

3 left

💡 Hint

Common Mistakes

Using different keys for provide and inject.

Forgetting to access the count property with .count.

The reactive object state is provided and injected using the same key 'stateKey'. Accessing injectedState.count shows the reactive count value.

Practice

1. What is the main purpose of using provide and inject in Vue?

easy

A. To define routes in a Vue application

B. To share data or functions between components without passing props manually

C. To handle component lifecycle hooks

D. To create global CSS styles for components

Solution

1. Step 1: Understand the role of provide/inject

   They allow sharing data or functions from a parent component to its descendants without passing props through every intermediate component.

2. Step 2: Compare with other options

   The other options relate to defining routes, creating global CSS styles, and handling component lifecycle hooks, which are unrelated to provide/inject.

3. Final Answer:

   To share data or functions between components without passing props manually -> Option B

4. Quick Check:

   Dependency injection = share data without props [OK]

Hint: Remember provide/inject shares data without prop drilling [OK]

Common Mistakes:

• Confusing provide/inject with props or events
• Thinking provide/inject manages styles or routing
• Assuming provide/inject replaces Vuex or global state

2. Which of the following is the correct syntax to provide a value in a Vue 3 component using the Composition API?

easy

A. const value = inject('key')

B. this.provide('key', value)

C. provide('key', value)

D. inject('key', value)

Solution

1. Step 1: Identify provide syntax in Composition API

   In Vue 3 Composition API, you call provide('key', value) inside setup() to share data.

2. Step 2: Check other options

   const value = inject('key') is for injection, not providing. this.provide('key', value) uses this which is not used in setup(). inject('key', value) is incorrect because inject does not provide values.

3. Final Answer:

   provide('key', value) -> Option C

4. Quick Check:

   Provide = provide('key', value) [OK]

Hint: Provide uses provide('key', value) inside setup() [OK]

Common Mistakes:

• Using inject instead of provide to share data
• Trying to call provide on this inside setup()
• Confusing provide syntax with options API methods

3. Given the following Vue 3 setup, what will be logged in the child component?

import { provide, inject } from 'vue';
const Parent = {
  setup() {
    provide('message', 'Hello from parent')
  }
}

const Child = {
  setup() {
    const msg = inject('message')
    console.log(msg)
  }
}

medium

A. null

B. undefined

C. An error because provide is missing a return

D. 'Hello from parent'

Solution

1. Step 1: Understand provide/inject behavior

   The parent provides the string 'Hello from parent' with key 'message'. The child injects this key and receives the value.

2. Step 2: Predict console output

   Since the child injects the provided key correctly, it logs 'Hello from parent'.

3. Final Answer:

   'Hello from parent' -> Option D

4. Quick Check:

   Inject returns provided value = 'Hello from parent' [OK]

Hint: Inject returns what provide shares by key [OK]

Common Mistakes:

• Expecting undefined if no return in setup
• Confusing provide with returning values
• Assuming inject returns null if key exists

4. What is wrong with this Vue 3 code snippet?

import { provide, inject } from 'vue';
const Parent = {
  setup() {
    provide('data', 123)
  }
}

const Child = {
  setup() {
    const data = inject('data')
    console.log(data)
  }
}

medium

A. inject is missing a default value, may cause undefined

B. provide is called outside setup()

C. provide must return an object

D. inject cannot be used in setup()

Solution

1. Step 1: Check provide usage

   Provide is correctly called inside setup() with key 'data' and value 123.

2. Step 2: Check inject usage

   Inject is called correctly but without a default value. If the key is missing, it returns undefined, which might cause issues.

3. Final Answer:

   inject is missing a default value, may cause undefined -> Option A

4. Quick Check:

   Inject without default can be undefined [OK]

Hint: Always provide default value to inject to avoid undefined [OK]

Common Mistakes:

• Thinking provide must return an object
• Believing inject can't be used in setup
• Assuming provide is outside setup here

5. You want to share a reactive object between a grandparent and a grandchild component using provide/inject in Vue 3. Which approach correctly ensures the grandchild reacts to changes in the shared object?

hard

A. Provide a reactive object using provide('state', reactiveObj) and inject it normally in the grandchild

B. Provide a plain object and inject it with a default value in the grandchild

C. Provide a reactive object but inject it inside onMounted hook in the grandchild

D. Provide a reactive object but convert it to a ref before injecting

Solution

1. Step 1: Understand reactive sharing with provide/inject

   Providing a reactive object directly shares its reactivity, so descendants see updates.

2. Step 2: Evaluate options for reactivity

   Provide a reactive object using provide('state', reactiveObj) and inject it normally in the grandchild correctly provides a reactive object and injects it normally, preserving reactivity. Provide a plain object and inject it with a default value in the grandchild uses a plain object, losing reactivity. Provide a reactive object but inject it inside onMounted hook in the grandchild delays injection unnecessarily. Provide a reactive object but convert it to a ref before injecting converts reactive to ref, which is unnecessary and may cause confusion.

3. Final Answer:

   Provide a reactive object using provide('state', reactiveObj) and inject it normally in the grandchild -> Option A

4. Quick Check:

   Reactive object provided and injected keeps reactivity [OK]

Hint: Provide reactive object directly to keep reactivity in inject [OK]

Common Mistakes:

• Providing plain objects losing reactivity
• Injecting inside lifecycle hooks unnecessarily
• Converting reactive to ref before injecting